This invention relates generally to clamps used for lifting and maneuvering a variety of standard structural workpieces. It is particularly suitable for selectively either turning a workpiece so that it rests on a new base after being lifted, or lifting a workpiece so that it rests on its original base after a lift. The clamp may also be used for lifting a plate and as a portable hanger.
Clamps which securely grip workpieces and which could be used as portable hangers exist in the prior art. An example of a clamp which securely grips workpieces, particularly plates, is that disclosed by U.S. Pat. No. 3,269,766. This prior art clamp includes a settable jaw having a convex cam to retain the workpiece. The convex cam is connected by an articulation to the end of a screw threaded through an arm of the clamp. Workpieces are retained between the convex cam and a second arm of the clamp. The clamp disclosed in U.S. Pat. No. 3,269,766 will not selectively turn the workpiece.
Clamps which selectively turn workpieces also exist in the prior art. They are used to rotate the workpiece from its freestanding original orientation, when it was unsupported by a clamp, through ninety degrees to rest on a new base. However, at least one of these clamps is not recommended for lifting plate, and it does not lock or secure the workpiece within the clamp unless a hoisting force is applied.
Standard structural workpieces exist in a wide variety of shapes such as flanged beams, angles, plates, channels and tubes. Each are encountered in various sizes, and composite structural elements may be fabricated from them, such as girders and angle beams. Structural shaped workpieces and composite structural elements must be maneuvered into position to facilitate their assembly in structures.
Typically a number of single purpose clamps are used to accomplish various maneuvers and purposes. Prior art clamps exist for maintaining flanged beams and girders in a balanced horizontal position. Others exist for vertical lifting of plate and of other structural shapes having vertical portions when freestanding. Some exist for horizontal lifts of plate and the like, but they must be used in pairs and are non-locking.
Multipurpose clamps are also used to accomplish various purposes. Locking clamps capable of horizontal lifts in pairs and intermittent vertical lifts are known. Also known are clamps which slide over a beam's horizontal flange for lifting, and can additionally be used as portable hangers.
No one of the prior art clamps is capable of satisfying all of the foregoing functions while positively locking the workpiece and yet be particularly suitable for selectively turning a variety of workpieces.